This invention provides a low cost means for achieving affordable solar energy by greatly reducing the cost of solar concentrators which increase (concentrate) the density of solar energy incident on the solar energy converter. A limiting factor in the utilization of solar energy is the high cost of energy converters such as photovoltaic cells. For example, for the purpose of generating electricity, a large area of expensive solar cells may be replaced by a small area of high-grade photovoltaic solar cells operating in conjunction with the inexpensive intelligent micro-optics of this invention. Thus the instant invention can contribute to the goal of achieving environmentally clean energy on a large enough scale to be competitive with conventional energy sources.
The rotatable elements of this invention are mirrored balls and cylinders. As derived in U.S. Pat. No. 6,612,705 of which the inventor of this instant invention is the co-inventor, balls in a square array have a packing fraction of 0.785 and 0.907 in an hexagonal array. Balls have an advantage over cylinders in that they can operate in either a single-axis or two-axis tracking mode. Cylinders have an advantage over balls in that they can have a packing fraction of nearly 1, but they are limited to a single-axis tracking mode.
The instant invention operates by the induced dipole alignment of solar concentrator balls such that the dipole that is induced in the dielectric material surrounding a mirror acts in harmony with the induced dipole in each mirror. An external applied electric field E induces a dipole by polarizing the dielectric to partially cancel the field E inside the dielectrc. In an applied electrostatic field, E, a dipole moment is induced in the metallic conducting material of the micro-mirrors because the charge distributes itself so as to produce a field free region inside the conductor. To internally cancel the applied field E, free electrons move to the end of each conducting mirror antiparallel to the direction of E, leaving positive charge at the end that is parallel to the direction of E. The electrostatic field induces and aligns the electrostatic dipoles of the dielectric and mirrors in a way somewhat analogous to an induced magnetic dipole in a pivoted ferromagnetic material in a magnetic field. When pivoted, a high aspect ratio (length to thickness ratio) ferromagnetic material becomes polarized and rotates to align itself parallel to an external magnetic field. Similarly an electrostatic field polarizes and aligns each dielectric ball and mirror. The mirror has a high aspect ratio of diameter to thickness. The ball is bifurcated into two semi-balls, each of which has a high aspect ratio of diameter to thickness.
If alignment is attempted in a conventional manner such as is used in Gyricon displays, the induced polarization electric dipole fields of mirror and dielectric ball presents a dilemma since it is perpendicular to the zeta potential produced dipole field and the net vector is in neither direction. The “zeta potential,” is the net surface and volume charge that lies within the shear slipping surface resulting from the motion of a body through a liquid. The zeta potential is an electrical potential that exists across the interface of all solids and liquids. It is also known as the electrokinetic potential. The zeta potential produces an electric dipole field when a sphere is made from two dielectrically different hemispheres due to their interaction with the fluid surrounding it. In the instant invention, no problem arises by making both semi-spheres (semi-balls) out of the same transparent material to eliminate or minimize the zeta potential. It would be quite difficult for Gyricon displays to make the surface of both hemispheres out of the same material because they require optically different surfaces e.g. black and white, or e.g. cyan, magenta, and yellow for color mixing.
The topic of the dipole interactions between balls seems not to have been discussed in the Gyricon patents and literature. A heuristic analysis shows that this is not a serious problem. The electric field strength of a dipole, Ed is proportional to 1/r3, where r is the radial distance from the center of the dipole. The energy in the field is proportianal to (Ed)2. Thus the energy of a dipole field varies as 1/r6. The force is proportional to the gradient of the field, and hence varies as 1/r7. With such a rapid fall off of the dipole interaction force, it can generally be made very small compared to the force due to the applied field E, and to the frictional forces that are normally present. Therefore interaction of the dipole field forces between mirrored elements (balls or cylinders) can generally be made negligible. The term “element” or “ball” will herein be used to represent the general concept of spheroids and cylinders. Although the primary application of the instant invention is for a solar concentrator application, there are a number of other applications such as mirrored illumination and projection, optical switching, solar propulsion assist, etc.
The 1998 Gyricon U.S. Pat. No. 5,717,515 of Sheridon, entitled “Canted Electric Fields for Addressing a Twisting Ball Display” is exclusively concerned with Displays. There appears to be no mention of any other application than directly viewed Displays, either specifically or by general statement. In this Sheridon patent, no mention is made of a mirror in the gyricon balls, nor is there any mention of specular reflection as would be obtained from a mirror. On the contrary, means are discussed to increase diffuse reflection from the balls so the Gyricon display may easily be observed from all angles. Certainly there is no anticipation of a solar concentrator application, mirrored illumination and projection, optical switching, solar propulsion assist, or any other micro-mirror application.
Furthermore Gyricon patents have no mention of coupling means to the balls other than by means of the zeta potential dipole, or an embedded electret dipole both of which are parallel to the Gyricon axis of symmetry which in the case of black and white balls goes through the vertex of the black hemisphere, the center of the sphere, and the vertex of the white hemisphere. Also there is no mention of an induced polarization electric dipole in the dielectric of their balls; and they have no mirrors in which to induce a dipole. Furthermore, their zeta potential dipole is parallel to the Gyricon axis of symmetry, whereas in the instant invention the induced polarization electric dipoles of dielectric and mirror are perpendicular to the axis of symmetry. Thus the application of the same electric field in the instant invention produces an entirely different orientation or alignment than in the Sheridon patent.
The instant invention differs substantially from that of Sheridon and from that of Goodrich U.S. Pat. No. 4,261,653 in the use of: mirrored elements (balls and cylinders); induced polarization electric dipoles in the mirrors and elements; the dipole fields being perpendicular to the axis of symmetry (rather than parallel); the use of fragmented wire electrodes to provide greater transparency; and the combination of fragmented wire electrodes and partitioned electrodes to provide greater transparency of the active surface than in the Sheriron patent.
The instant invention is primarily concerned with method and apparatus for the alignment of solar concentrator micro-mirrors. However, it has broader applications wherever mirrors are used for focussing such as for solar propulsion assist, illumination and projection of light, optical switching, etc.